A friend who is a retired university professor tells the story that he used to begin each unit with a short lesson on the difference between its and it’s. He’d warn his students to listen carefully because every time they made an its/it’s error in their assignments, he would be deducting a 1% penalty mark. He swears it made a difference—but also said there were always students who had to pay his rather high price.
If you have difficulty with this one, here’s a recap, with a couple of easy guidelines:
its is a possessive, the neutral equivalent of his or her.
If you can’t replace its with his or her (leaving the gender issue aside!), you probably mean it’s.
Mary is publishing her novel. Wally is publishing his memoir. The company is publishing its annual report.
it’s is a contraction meaning it is or it has.
If you can’t replace it’s with it is or it has, you probably mean its.
It’s not unusual. [It is not unusual.]
It’s always been this way. [It has always been this way.]
So, to return to that clichéd title with the grandiose claim:
It’s worth its weight in gold means It is worth the weight of it in gold—but you knew that, didn’t you?
Give it a try next time you’re proofreading. And let’s all be thankful that editors don’t apply penalties.